Microwave coagulation applicator and system with fluid injection

ABSTRACT

A microwave applicator for insertion into living body tissue for use in microwave coagulation and ablation treatments includes a microwave transmission line extending between an attachment end of the applicator and an antenna toward an insertion end of the applicator with an outer conductive sleeve forming an enclosed fluid space around the transmission line. A fluid circulation system circulates fluid in the fluid space. A portion of or all of the circulating fluid can be injected into tissue that surrounds the applicator body from approximately the proximal end of a desired heating zone produced by microwave energy radiated from the antenna along the applicator body toward the proximal end of the applicator to hydrate and wet the tissue outside the proximal end of the desired heating zone to reduce the drying of this tissue and limit extension of the heating and ablation zone proximally along the applicator body.

RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 12/620,002, filedNov. 17, 2009, now U.S. Pat. No. 8,414,570, and of application Ser. No.12/689,195, filed Jan. 18, 2010, now U.S. Pat. No. 8,551,083, bothentitled Microwave Coagulation Applicator and System, and both herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

Field

This invention relates to electromagnetic radiation (EMR) therapy andmore particularly to applicators and systems for applyingelectromagnetic energy to a treatment site in a living body to heattissue needing treatment at the treatment site. The invention is usefulparticularly for treatments in the nature of microwave coagulation orablation. A limitation found in current microwave antennas that are usedfor microwave coagulation and ablation is that the energy distributionpattern generally extends back along the applicator from the proximalend of the desired coagulation and ablation zone around the microwaveenergy radiating portion of the applicator toward the proximal end ofthe applicator. This undesirably extends the coagulation and ablationzone along the applicator toward the proximal end of the applicatorbeyond the tissue desired to be coagulated or ablated. This results inan elliptical or tear drop heating pattern shape where the desired shapefor the energy distribution pattern and the coagulation and ablationzone is generally more spherical.

State of the Art

The use of electromagnetic (EM) energy to heat tissue for the treatmentof disease is known. In using microwave energy for tissue heating, anapplicator having a microwave radiating antenna is positioned withrespect to the tissue to be treated (heated) so that microwave energyradiated from the antenna penetrates and heats the tissue. Manymicrowave applicators are known in the art. Death, or necrosis, ofliving tissue cells occurs at temperatures elevated above a normal celltemperature for a sufficient period of time. The sufficient period oftime is generally dependent upon the temperature to which the cells areheated. Above a threshold temperature of about 41.5 degrees C.,substantial thermal damage occurs in most malignant cells. Attemperatures above about 45 degrees C. thermal damage occurs to mostnormal cells. During treatment, it is desirable to produce an elevatedtemperature within the targeted tissue for a time period sufficient tocause the desired cell damage, while keeping nearby healthy tissue at asafe lower temperature. For this reason, when treatment involving tissueheating is used, it is important to assure both adequate tumor heatingthroughout the tumor to the tumor margin and reduced temperatures in thecritical normal tissue.

Heating therapy is sometimes combined with other treatments, such assurgery, ionizing radiation, and chemotherapy. For example, when heatingis combined with radiation, it is desirable to maintain the temperaturewithin the diseased tissue within the range of about 42 to 45 degrees C.Higher temperatures are usually undesirable when a combined treatmentmodality is used because higher temperatures can lead to microvessalcollapse causing resistance to radiation therapy and decrease the amountof systemic chemotherapy from reaching the tumor if it has vasculardamage. Lower temperatures are undesirable because they can fail toprovide adequate therapeutic effect. Therefore, it is important tocontrol the temperature within the desired range for multi-modalitytreatments and not allow heating of the tissue in the tumor or aroundthe tumor to above 45 degrees C. if such tissue damage from othertreatments may be compromised. Treatment within this controlledtemperature range is usually referred to as hyperthermia.

Forms of thermal therapy that kill the tissue with heating alone aregenerally referred to as coagulation or ablation. To adequatelyeradicate a cancerous tumor with only the application of heat, it isnecessary to ensure adequate heating is accomplished throughout theentire tumor. In cases of a malignant tumor, if viable tumor cells areleft behind, the tumor can rapidly grow back leaving the patient withthe original problem. In what is generally referred to as microwavecoagulation or microwave ablation, the diseased tissue is heated to atleast about 55 degrees C., and typically above about 60 degrees C., forexposure times sufficient to kill the cells, typically for greater thanabout one minute. With microwave coagulation and ablation treatments,there is a volume reduction of temperature that ranges from the hightemperature in the treated tissue to the normal tissue temperature of 37degrees C. outside the treated tissue. The outer margin of the overallheat distribution in the treated tissue volume may then result in damageto normal tissue if such normal tissue is overheated. Therefore, forprolonged coagulation or ablation treatments where the coagulation orablation volume is maintained at very high temperatures, there is a highrisk of damage to surrounding normal tissues. For proper treatment oftargeted cancerous tumor volumes or other tissue volumes to be treated,it becomes very important to properly deliver the correct thermaldistribution over a sufficient time period to eradicate the tumor tissuewhile minimizing damage to critical surrounding normal tissue.Fortunately, there are tumor locations that reside in normal tissue thatcan be destroyed by the heating in limited areas without affecting thehealth of the patient, such as liver tissue. In such situations thecoagulation can be applied in an aggressive way to include a margin ofsafety in destruction of limited surrounding normal tissues to assurethat all of the cancerous tumor is destroyed.

The process of heating very rapidly to high temperatures that is commonin coagulation and ablation treatments may utilize a rather shortexposure time. In doing so, the resulting temperature distributionbecomes primarily a result of the power absorption distribution withinthe tissue. However, if such treatments continue for multiple minutes,the blood flow and thermal conduction of the tumor and surroundingtissues will modify the temperature distribution to result in a lesspredictable heat distribution because the changes occurring in bloodflow in such a heated region may not be predictable. Thus, it isimportant to optimize the uniformity of the tissue heating power that isabsorbed to lead to a more predictable temperature distribution thatbetter corresponds with the treatment prescription. Therefore,pretreatment planning practices prior to and possibly during treatmentfor calculating the power and temperature distribution resulting fromthe parameters of power and relative phase of the power applied to thetissue can be important for not only coagulation and ablation, but alsohyperthermia. As higher temperatures are used during treatment, it mayincrease patient discomfort and pain, so it can be helpful to avoidexcessive temperatures to reduce the need of patient sedation.

Invasive microwave energy applicators can be inserted into living bodytissue to place the source of heating into or adjacent to a diseasedtissue area. Invasive applicators help to overcome some difficultiesthat surface applicators experience when the target tissue region islocated below the skin (e.g., the prostrate). Invasive applicators mustbe properly placed to localize the heating to the vicinity of thedesired treatment area. Even when properly placed, however, it has beendifficult to ensure that adequate heat is developed in the diseasedtissue without overheating surrounding healthy tissue. Further, withapplicators operating at higher power levels to produce the neededhigher temperatures for coagulation and ablation, there is a tendencyfor the coaxial cable in the portion of the applicator leading fromoutside the body to the location of the radiating antenna in theapplicator to heat to undesirably high temperatures which can causethermal damage to the normal tissue through which the applicator passesto reach the diseased tissue to be treated. Therefore, various ways ofcooling the applicator have been used in the prior art.

In the use of radiofrequency (RF) electrodes in the prior art, a primaryelectrode is invasively inserted into the body while a secondaryelectrode is either invasively inserted into the body such as in abipolar RF applicator or separately at another location or is placed onthe skin outside the body so that radio frequency heating currents passfrom the primary electrode to the secondary electrode. In this process,the tissue around the primary electrode has the tendency to dry out andchar. When the tissue around the primary electrode that needs to passthe RF heating currents to the secondary electrode dries, the drying ofthe tissue around the electrode provides high electrical resistance toimpede the flow of heating current. This drying of the tissue thenlimits the flow of current from the primary electrode out into thetissue beyond the dry or charred tissue thereby limiting the tissuecoagulation zone to that which is achieved prior to the formation ofthis dry or charred tissue around the electrode. A technique has beendeveloped to infuse fluid, such as saline solution, from the tip of suchprimary RF electrode to permit the tissue fluids to be replaced as theyare being heated in that region, thereby reducing the resistance tocurrent flow by maintaining the wetness and the electrical conductivityof the tissue near the electrode. This allows continued desired flow ofcurrent from the primary electrode to produce the desired tissue heatingand coagulation. Examples of this are shown in U.S. Pat. Nos. 6,066,134,6,112,123, and 6,131,577. It is also known in the art that fluids, suchas saline solution, can be used with microwave antennas where theinfusion of the fluids, such as saline, is introduced into the primaryheating region to aid in the maintenance of the radiation impedance ofthe antenna by replacing the fluids in the tissue in the area of primaryradiation and heating. Examples of this are shown in published patentapplications 2006/0122593 and 2009/0248006. Other methods are alsoutilized to improve the impedance matching during microwave coagulationof tissue such as tuning changes by frequency change (U.S. Pat. No.7,594,913) and variation of the exposed radiating antenna tip (publishedapplication 2009/0131926).

It is also known that with microwave energy applicators, the radiatedenergy forms a tear-drop type heating pattern with a tail extending backalong the applicator shaft from the desired tissue heating zone into thenormal tissue along the applicator insertion path toward the proximalend of the applicator. In some instances, the extent of the tail changesduring treatment and with the positioning of the applicator, such aswith the insertion depth of the applicator. The forming of this heatedtail and the alteration of the coagulation zone as a function ofvariable insertion depths is not a desirable result as the coagulationzone should be consistent at various reasonable insertion depths, andthe heating zone produced by the applicator is desirably a morespherical shape to produce a more spherical ablation zone.

While many microwave applicators are known in the art for applyingmicrowave energy to tissue to provide heating to the tissue, there is aneed for better applicators that are easy to use, have more consistentand predictable heating and coagulation patterns, and particularly thatare able to limit the length of the energy absorption pattern and theheating zone to limit the elongation along the applicator proximallyfrom the desired heating zone to therefore provide, when used forcoagulation or ablation, a more spherical coagulation or ablation shape.

SUMMARY OF THE INVENTION

The inventors theorize that the tail of the heating zone produced by amicrowave antenna which is caused by microwave energy extending alongthe applicator toward the proximal end of the applicator from theproximal end of the desired heating zone, and the often continuingextension of this tail along the applicator during the application ofmicrowave energy, is caused by the drying of the tissue, first in thedesired heating and ablation zone around the microwave antenna, and thenalong the applicator body from the desired heating zone toward theproximal end of the applicator. The theory is that as the tissue driesaround the desired heating zone, the dielectric constant of the tissuedecreases and the wavelength of the microwave energy in the tissueincreases. As the wavelength of the microwave energy in the tissueincreases, the area heated by the energy increases along the applicatortoward the proximal end and causes heating of the tissue in this newarea into which the longer microwaves are extending. This heating driesthis tissue to further extend the wave length of the microwaves in thisarea which further extends the heating area along the applicator shaft,thus heating more and more of the tissue along the applicator shafttoward the proximal end of the shaft along the insertion path of theapplicator. In addition, or alternately, when the tissue dries andreduces the dielectric constant value of the tissue, there is a higheramount of the radiated electric field that is concentrated in the dryingtissue that surrounds the proximal outer portion of the applicator,which outer portion is usually formed by a metal outer shaft. This isdue to the fact that the distribution of the electric field that isperpendicular to the metal of the metal shaft and is inverselyproportional to the value of the dielectric constant of the respectivetissue, varies with the boundaries between the wet and dry tissue. Thismeans that the electric field lines that pass perpendicularly throughthe drying tissue layers to the perpendicular metal shaft are altered intheir distribution relative to the tissues. For example, if thedielectric value of the tissue around the shaft is reduced by a factorof 10, as can be caused by charring, there would be a factor of 10increase in the electric field strength in that dry and charred regionthat would not be attenuated as rapidly compared to that of non-drytissues as it propagates along the outer metal body of the applicatortoward the proximal end. This could further increase the length of thetapering tail of the heating or ablation zone in the tissue along theproximal body portion of the applicator.

According to the invention, the inventors have found that by supplyingfluid, such as a saline solution, to the tissue along the applicatorshaft extending from approximately the proximal end of the desiredheating zone toward the proximal end of the applicator to replace thefluid in such tissue and preventing the drying of such tissue, that thetail of the heating zone is limited and that it is maintainedsubstantially constant rather than increasing with increased heatingtime. Thus, by injecting fluid into the tissue along the applicatorshaft extending from approximately the proximal end of the desiredheating zone toward the proximal end of the applicator, the tissue inthis area maintains its moisture content and limits the distance thetail extends along the applicator and substantially prevents thecontinuing elongation of the tail during the heating time. As a result,the heating and ablation zone becomes less tear drop shaped and morespherical shaped. This occurs without the necessity of injecting fluidinto the desired heating zone and even though the tissue in the desiredheating zone therefore will dry during heating. With fluid injectioninto the tissue in the area indicated outside and proximal to thedesired heating zone, the applicator can be designed and tuned toproduce a substantially constant heating and ablation zone. Fluid can besupplied to the tissue in various ways. If the applicator includes anapplicator fluid cooling system, the fluid injected into the tissue maybe a portion of the cooling fluid from the applicator cooling systemthat is directed from the cooling system into the tissue, or, with orwithout a fluid cooling system, fluid may be provided specifically anddirectly to the tissue to keep it in a moistened condition.

An embodiment of microwave applicator according to the invention for usein microwave coagulation and ablation treatments includes an elongateapplicator body having an insertion (distal) end for insertion into atissue region of a living body and an attachment (proximal) end forattachment to a source of microwave energy. An antenna for radiatingmicrowave energy into tissue to be treated to produce a desired heatingand ablation zone in the tissue is disposed toward the insertion end ofthe elongate applicator body. A coaxial microwave energy transmissionline is disposed within the applicator body to conduct microwave energyfrom the attachment end of the applicator to the antenna. In order tolimit the extent to which the microwave energy extends along theapplicator from approximately the proximal end of the desired heatingand ablation zone toward the proximal end of the applicator, therebylimiting the usual tail of the heating and ablation zone along theapplicator toward the proximal end of the applicator, fluid can beinjected along the applicator from approximately the proximal end of thedesired heating zone a distance along the applicator body toward theproximal end of the applicator. By injecting fluid in this tissueregion, tissue moisture and a higher dielectric constant is maintainedin the tissue to maintain a higher microwave loss factor so that themicrowave energy radiated into this tissue region is more rapidlyattenuated as it travels along the outside of the inserted applicator.This feature aids in providing a more spherical coagulation pattern byreducing the energy that extends along the applicator extending throughthe tissue region that is not intended to be heated.

In one embodiment of the applicator which includes a fluid coolingsystem, an outer conductive sleeve forms the outside of a portion of theapplicator body and is spaced concentrically around the microwave energytransmission line to form a cooling fluid space between the insidesurface of the outer conductive sleeve and the outer surface of themicrowave energy transmission line. The cooling fluid space extends fromthe proximal end of the applicator to the approximate proximal end ofthe desired heating and ablation zone. Because cooling is not normallyneeded in the tissue to be heated during coagulation and ablationtreatments, cooling is not provided in the area of the radiating antennaof the applicator where the heating of tissue is desired. A guide sleeveis positioned concentrically within the cooling fluid space and spacedinwardly from the outer conductive sleeve and around the outside of andspaced outwardly from the microwave energy transmission line. The guidesleeve guides flow of a circulating cooling fluid along the outsidesurface of the microwave energy transmission line and the inside surfaceof the outer conductive sleeve to cool the microwave energy transmissionline and the conductive outer sleeve to maintain the portion of theapplicator extending between the outside of the living body and thetissue to be treated in the living body at a temperature below thatwhich will damage healthy tissue. For fluid injection, the distal regionof the cooling fluid space may be configured with one or more openingsthrough the outer conductive sleeve to permit a portion of the coolingfluid that circulates in the cooling fluid space to leak into or beinjected into the tissue surrounding this region that is proximal to thedesired heating and ablation zone to reduce the drying out of tissue inthat region. This reduces the formation of the tear-drop type tailextending from the desired heating and ablation zone around the antenna.The added fluid in the tissue proximal the desired heating and ablationzone maintains a higher tissue moisture content in that proximal regionwhich maintains a higher tissue dielectric constant in that region andhigher microwave loss factor so that the portion of the microwave energyradiated is more rapidly attenuated as it travels along the outside ofthe inserted shaft. This provision of fluid to the tissue thereby limitsthe energy that extends along the applicator proximally from the desiredheating and ablation zone into the area not intended to be heated, solimits the creation of the heated tail and results in a more sphericalheating and ablation pattern.

With the fluid cooled applicator, a pump is generally provided tocirculate the cooling fluid through the cooling fluid space. The fluidpressure of the pump will generally provide sufficient hydraulicpressure to force a small amount of fluid through the openings throughthe outer conductive sleeve into the tissues. The typical flow rate ofcooling fluid in the cooling fluid space within the applicator body isin the range of 20 to 40 ml/minute. The rate needed to infuse fluid intothe tissue in the inserted proximal portion of the applicator would bein the range of less than 10 ml/minute and typically in the range of 1to 6 ml/minute. Therefore, there is ample flow to permit such a smallvolume to pass into the tissue without significant changes to theapplicator shaft cooling system and the inner circulation of coolingfluid through the applicator. A temperature sensor is positioned tomeasure the approximate temperature of the circulating cooling fluidthereby indicating that cooling fluid is actually circulating in thecooling fluid space and that the microwave energy transmission line andthe outer conductive sleeve are being actively cooled during themicrowave coagulation or ablation treatment. By monitoring theapproximate temperature of the cooling fluid, the heating of the tissuealong the insertion track of the applicator where inserted into theliving body to the diseased tissue can be better controlled to ensurethat damage to surrounding normal tissue is minimized during treatments.Further, when fluid is injected into the tissue from the cooling fluidcirculation system, confirmation of circulation of cooling fluid alsoconfirms that fluid is being infused or injected into the tissuesurrounding the portion of the applicator proximal the desired heatingand ablation zone.

Alternately, rather than circulating cooling fluid in the applicator,infusion of fluid into the tissue may be provided by eliminating thefluid flow return path either by blocking the fluid return path orremoving the fluid return path inside the applicator body, or byproviding a direct fluid flow path opening to the tissue, and providingeither a lower flow rate pump to provide the fluid directly to thetissue or by providing a fluid gravity drip line that is typical ofintravenous (IV) fluid applications. In such a case the fluid flow ratecan be set to a predetermined flow rate that would be typically in therange of 1 to 6 ml/minute.

In one embodiment of the present invention, a microwave applicator forheat treatment of diseased tissue within a living body includes a handleby which the applicator can be held and manipulated for insertion intothe living body. An elongate applicator body having an insertion end forinsertion into a tissue region of the living body extends from thehandle which usually forms the attachment end of the applicator. Anantenna is disposed toward the insertion end of the applicator body.Microwave energy is conducted from the handle to the antenna via amicrowave energy transmission line in the form of a coaxial cabledisposed within the applicator body. The coaxial cable includes an innerconductor and an outer conductor separated by a dielectric materialtherebetween. An outer conductive sleeve extends from the handle to aninsertion end of the outer conductive sleeve which is separated from theconductive tip by a gap, usually filled with a dielectric material. Theoutside diameters of the insertion tip, the outer conductive sleeve, andthe dielectric material filling the gap therebetween are all about equalso as to form a substantially smooth continuous elongate applicatorbody, for insertion into the living body. The elongate applicator body,or at least the portion thereof to be inserted into a living body, maybe coated with a stick resistant dielectric material such as Teflon.This can at least partially reduce the sticking of coagulation tissue tothe applicator outer surface, particularly in the areas of tissuecoagulation and ablation, to facilitate removal of the applicator aftertreatment. However, in one embodiment of the applicator, a portion ofthe dielectric material separating the conductive tip and the outerconductive sleeve remains exposed for direct contact with heated tissue.The dielectric material is a material, such as PEEK(polyetheretherketone), that heated tissue will stick to. This is arelatively small area along the applicator, but upon heating, the tissuewill stick to this dielectric material and such sticking will stabilizethe applicator to keep it in position during treatment of the tissue.When removal of the applicator is desired, the applicator can berotated, such as through between thirty and forty-five degrees ofrotation, to release the tissue and permit removal of the applicator.

In the illustrated example embodiment, the elongate applicator bodyextending from the handle will be substantially rigid. The outerconductive sleeve may be made of a metal such as stainless steel. Theconductive insertion tip of the applicator will also be metal, such asbrass or stainless steel, and may be sharpened sufficiently so that theapplicator can be inserted directly into tissue to be treated. However,even when sharpened, the applicator will generally not be inserteddirectly through the tough tissue of the skin, but will usually requirethat a cut or an opening, such as made by a hypodermic needle insertedthrough the skin, first be made and then the applicator is insertedthrough such cut or opening. Further, in an illustrated exampleembodiment, a conductive metal shunt is positioned at the insertion endof the conductive outer sleeve to extend toward the insertion tip. Theshunt is also electrically coupled to the outer conductor of themicrowave energy transmission line, thereby electrically coupling theouter conductor of the microwave energy transmission line to theconductive outer sleeve. The insertion tip is secured to, but separatedfrom, the insertion end of the shunt by a substantially rigid dielectricspacer that has structural stiffness to prevent bending of the jointbetween the shunt and tip and to electrically insulate the tip, which iselectrically coupled to the microwave energy transmission line innerconductor, from the shunt, which is electrically coupled to themicrowave energy transmission line outer conductor. The substantiallyrigid dielectric spacer is bonded to the shunt and applicator tip, suchas by an epoxy adhesive. In another illustrated example embodiment, theshunt is not used and the dielectric material connects the conductivetip to the outer conductive sleeve. In this example embodiment, theouter conductive sleeve is electrically insulated from both the outerconductive tip and the outer conductor of the microwave energytransmission line.

A non-conductive guide sleeve extends from the handle and is positionedconcentrically within the elongate applicator body inside and spacedinwardly from the outer conductive sleeve and around the outside of andspaced outwardly from the microwave energy transmission line, i.e.,outwardly from the outer conductor thereof. The guide sleeve guides flowof a circulating cooling fluid from the handle along the outside surfaceof the coaxial microwave transmission line to the end of the guidesleeve toward the insertion end of the applicator, around the end of theguide sleeve, and back along the inside surface of the outer conductivesleeve to the handle. An opposite flow of the cooling fluid can also beused. Circulation of cooling fluid cools the coaxial microwavetransmission line and the conductive sleeve to maintain the portion ofthe applicator extending between the outside of the living body and thetissue to be treated in the living body at a temperature below thatwhich will damage healthy tissue. If fluid injection into tissue isdesired, the outer conductive sleeve and/or the shunt may be providedwith one or more openings therethrough to allow a portion of the coolingfluid when circulating in the applicator to flow from the applicatorinto the tissue surrounding the applicator adjacent the proximal end ofthe desired heating and ablation zone created by the applicator andextending a distance from the proximal end of the desired heating andablation zone toward the proximal end of the applicator. The one or moreopenings are sized and positioned so as to allow substantially apredetermined amount of fluid flow into the tissue during fluidcirculation in the applicator to maintain moisture in the tissue duringoperation of the applicator. A temperature sensor is positioned, such asin the handle, to measure the approximate temperature of the coolingfluid being circulated in the applicator. The temperature of the coolingfluid in the applicator is an indication of whether or not the fluidcirculation system is operating and whether it is cooling sufficiently.

Supply and return connections for the cooling fluid from a pressurizedsource of cooling fluid, usually through flexible hoses, are provided inthe handle. Also, a connection to connect to a source of microwavepower, such as through a flexible coaxial cable, is also provided in thehandle. The handle serves as an interface between the more flexiblecoaxial cable extending from a microwave generator and the more flexiblefluid hoses from a source of cooling fluid, and the substantial rigidelongate applicator. In one example embodiment, a sheath is provided toenclose the hoses and flexible coaxial cable as they extend from thehandle to keep them together and make handling of the applicator easier.An embodiment of the sheath material is a plastic braid material thatwill tighten around the enclosed hoses and coaxial cable when stretched.

The temperature sensor used in the applicator may be a thermistor. Theresistance of a thermistor varies with the temperature of thethermistor. The temperature measured by the thermistor is obtained by anexternal circuit that measures the temperature by causing a constant dccurrent to flow through the thermistor. The resistance of the thermistorthen produces a dc voltage that is indicative of the temperature of thethermistor. The temperature sensor in the handle, or a temperaturesensor positioned along the applicator, may be coupled to the flexiblecoaxial cable extending from the microwave generator through a couplingnetwork, such as a resistive and capacitive coupling network. Theresistive and capacitive coupling network allows a dc current from thecoaxial cable conductors to flow to and from the thermistor whileisolating the thermistor from the microwave power signals, and allowsthe microwave power signals to flow to the antenna while isolating theantenna from the dc current. Similarly, a coupling network can be usedat the opposite end of the flexible coaxial cable, such as in powersplitting and multiplexing circuitry, to separate the dc temperaturesignals from the flexible coaxial cable conductors and direct them totemperature sensing circuitry in a system controller while isolating thetemperature sensing circuitry from the microwave power signals, andpassing the microwave power signals from the system microwave generatorwhile isolating the system microwave generator from the dc temperaturesignals. The use of a computer in the system controller to sense forwardpower, reflected power, measure the thermistor temperature, and possiblymonitor other variables such as monitoring tissue temperature by one ormore independently inserted temperature sensors, provides control andfeedback for the applied microwave power and the proper safety andoperation of the microwave coagulation or ablation procedure.

In addition to the temperature sensor to measure the approximatetemperature of the cooling fluid line in the applicator, one or moretemperature sensors may be placed along the elongate applicator body soas to place the one or more temperature sensors at positions to measurethe temperature of the tissue of the living body along the applicator.If such additional temperature sensors are provided, it is usuallyadvantageous to position one of such temperature sensors at a positionclose to an expected outer margin of the desired or allowable heatingarea in the living body tissue to be heated by the antenna duringoperation of the applicator. This can be used to provide a warning ifthe tissue to be protected outside the margin of the area to be treatedis approaching an undesirably high temperature. It can also be used toestimate the location of the outer margin of the effective heated volumeduring treatment.

The use of phased arrays can also reduce microwave heating along theshafts of the applicators due to cross coupling of the energy betweenthe antennas that are driven in phase and separated by a distance thatprovides for partial power cancellation along the outer portion of theinserted applicators and an increase in tissue heating between theseinserted applicators. This partial power cancellation is accomplishedwhen the distance between approximately parallel inserted antennas isapproximately a half of a wavelength so that the cross coupled energy issomewhat out of phase with that on an antenna due to its own radiatedenergy. For a frequency of 915 MHz, for example, the wavelength intypical high water content tissues, such as muscle and tumor tissues, isapproximately 4.3 to 4.7 cm. This means that for an insertion separationof 2.1 to 2.4 cm the separation is about right for this 180 degreerelationship. There is also cross coupled phase cancellation forsignificant phase differences other than 180 degrees, for example, a 135or 225 degree phase difference will still provide partial phasecancellation from the cross coupling of the microwave coupled fields topartially cancel microwave energy along the outer portion of theinserted applicators. This would be consistent with an applicatorspacing of between about 1.6 to 3.0 cm for the 915 MHz example. Thispartial cancellation of microwave power around the inserted shaftsresults in reduced heating along the inserted shafts during activemicrowave tissue heating. This also reduces the local power fieldslocally around the radiating antennas and the outer shafts to reducetissue sticking to the antennas and shafts.

The control of the heating may further include the systematic use ofapplicators in phased arrays with optimization computational guidance inthe form of pretreatment planning to provide an ideal insertion patternand power and phase application to the array of applicators to produceand control improved uniformity of power deposition, temperatures,and/or coagulation of tissue throughout the tumor volume, andparticularly at the tumor margins. The treatment is thereby optimizedand controlled by the aid of a numerical calculation of either theplanned insertion pattern and number of antennas or the actual patternachieved as indicated by various non-invasive imaging processes such ascomputer tomography (CT), ultrasound, or magnetic resonance imaging(MRI). It also may be feasible to use such planning information toadjust power amplitude and phase of each of the inserted applicators asdirected by a computer-controlled system using the predicted powerpatterns from the computer numerical model.

In a phased array embodiment of the invention, a single microwavegenerator is used to provide the microwave power for all applicators.The generator will usually operate at 915 MHz, which is an emissionfrequency commonly licensed for medical applications. This singlegenerator is connected to a passive, non-switching, microwave impedancematched power splitter (divider) which is used to direct powersimultaneously to multiple ports that are connected to one or moremicrowave dipole antennas such as described for the above describedapplicators. This arrangement provides approximately equal powersimultaneously to each of the output connection ports. This arrangementalso provides equal phase output of the microwave energy at each of theoutput ports. Thus, when multiple antennas are connected to the ports ofthe power splitter, they have equal power and equal relative phase andare thus correctly called a phased array of antennas. The cables goingto the radiating points on each antenna are maintained at the sameelectrical length so that the radiated energy from the antennas arephase synchronous and phase coherent. Phase synchronous meaning thatthere is a fixed phase relationship between the radiation phase of allantennas and phase coherent meaning that the relative radiated phasefrom each antenna is approximately the same. The use of phased arrays asdescribed increases the heating in the spaces between the antennas byproviding improved uniformity of the coagulation of the targeted tissueproviding more power absorption than when using channel switching andother non-phase synchronous and non-simultaneous channel operationmethods.

When using a phased array of applicators, the applicator antennas areinserted in approximately a pattern than corresponds with equal spacingalong the circumference of an insertion circle around the tissue to betreated. This provides for approximately equal spacing between theantennas along the perimeter of an insertion pattern. Thus, a pattern oftwo antennas would be inserted at a distance of separation that wouldrepresent the diameter of an insertion circle. Three antennas would forma triangle pattern as they are approximately equally spaced around thecircumference of a circular insertion pattern. Four antennas would forma square pattern. The antennas should be approximately parallel asinserted with the central point of the radiation from each antennainserted to approximately the same depth position with respect to thetissue to be treated so as to have the radiation feedpointsapproximately aligned side by side.

As indicated, the applicator of the invention can be used as a singleapplicator inserted into the diseased tissue, or as an array of morethan one applicator positioned in or around the diseased tissue. Inorder to provide the most efficient transfer of microwave energy fromthe microwave generator to the tissue to be treated, the flow paths ofthe microwave energy from the microwave generator to the applicatorantennas should be impedance matched and tuned for the number ofapplicators used. This can require different systems with differentpower splitters when a single applicator is used or when multipleapplicators are used to form an array. The present invention can providea special power splitter circuit so that a single system can be used fora single applicator or for a plurality of applicators. According to theinvention, at least one power splitter circuit is provided for couplingthe microwave energy generator to at least one coaxial microwave energysupply cable for supplying microwave energy from the microwave generatorto the microwave applicator. The at least one power splitter circuit hasa microwave power input connected to the microwave generator and aplurality of output ports, wherein one of the plurality of output portsis a single connection output port for use where only a single coaxialmicrowave energy supply cable and microwave applicator is connected tothe power splitter circuit, and the remaining output ports of theplurality of output ports are multiple connection output ports for usewhere two or more coaxial microwave energy supply cables and microwaveapplicators are connected to two or more multiple connection outputports of the power splitter circuit. The single connection output portis impedance matched and tuned to provide efficient energy transfer whenusing a single applicator and the multiple connection outlet ports areimpedance matched and tuned to provide efficient energy transfer whenusing a number of applicators anywhere from two to the total number ofmultiple connection output ports provided. In this way, if a singleapplicator is used, it is connected to the single connection outputport. If multiple applicators are used, each of the multiple applicatorsis connected to a different multiple connection output port and nothingis connected to the single output port.

Means can be provided to detect whether or not there is an antennaconnected to a particular microwave power output port, and whether suchantenna is connected to a correct port. This can be done if thermistoror other resistive temperature sensors are used in the applicators, aspreviously described, and the substantially dc temperature sensorsignals are transmitted to the system controller through the coaxialpower supply cable. In such instance, the system controller can detectwhich of the output ports have applicators attached by detecting whethertemperature sensors signals are present at such output ports. Bydetecting the number of applicators attached to output ports of a powersplitter circuit and to which of the output ports they are attached, thesystem controller can determine if a single applicator is connected, andif so, whether it is properly connected to the single connection outputport, or whether two or more applicators are connected, and if so,whether they are all properly connected to multiple connection outputports. The system controller can provide an alarm signal if one ofmultiple applicators is attached to the single connection output port orif a single applicator is connected to one of the multiple output ports.

Further, when using multiple fluid cooled applicators in which coolingfluid is circulated through the applicators and, in embodiments in whichfluid is injected into tissue surrounding a portion of the applicatorsfrom the fluid cooling system or when fluid is injected directly intothe tissue from the applicators without a cooling fluid circulationsystem, it is necessary to provide a source of cooling fluid and areturn line for cooling fluid for each of the applicators, or merely asource fluid for injection into the applicators for injection into thetissue. In order to make connection of a variable number of applicatorsquick and easy, the invention can provide a cooling fluid circulationsystem adapted to connect to and provide cooling fluid circulation for asingle applicator up to a preset number of multiple applicators. Such acooling fluid circulation system or an injection fluid supply system ofthe invention includes a plurality of cooling fluid supply connectorseach adapted to be connected to an individual applicator cooling fluidinlet and, if return of cooling fluid is contemplated, an equalplurality of cooling fluid return connectors each adapted to beconnected to an individual applicator cooling fluid outlet. Each of theplurality of cooling fluid supply connectors includes a normally closedshut off valve which opens when connected to an applicator cooling fluidinlet. This shut off valve prevents flow of fluid from the cooling fluidsupply connector except when connected to a cooling fluid inlet. Each ofthe plurality of cooling fluid return connectors, if provided, includesa one way flow valve allowing flow of fluid only into a cooling fluidreturn connector. This prevents fluid flow out of the system through acooling fluid return connector, but will allow return fluid to flow intothe system through such connector when connected to an applicatorcooling fluid outlet.

With this cooling fluid circulation system, when only a singleapplicator is used, one of the plurality of cooling fluid supplyconnectors is connected to the cooling fluid inlet of the singleapplicator and one of the plurality of cooling fluid return connectorsis connected to the cooling fluid outlet of the single applicator. Thiswill provide flow of cooling fluid through the single applicator. Nocooling fluid will flow through any of the cooling fluid supplyconnectors or the cooling fluid return connectors that are not connectedto the applicator. When a plurality of applicators is used, one of theplurality of cooling fluid supply connectors is connected to the coolingfluid inlet of one of the plurality of applicators, and one of theplurality of cooling fluid return connectors is connected to the coolingfluid outlet of one of the plurality of applicators. This will provide acooling fluid supply connector connected to each of the applicatorcooling fluid inlets and a cooling fluid return connector connected toeach of the applicator cooling fluid outlets and thereby provide a flowof cooling fluid through each of the plurality of applicators attachedto the system. Any number of applicators up to the number of coolingfluid supply connectors in the fluid supply system can be connected tothe fluid supply system. Again, no cooling fluid will flow through anyof the cooling fluid supply connectors or the cooling fluid returnconnectors that are not connected to the applicator.

One embodiment of cooling fluid circulation system can also include acooling fluid reservoir, a pump connected to pump cooling fluid from thecooling fluid reservoir to the plurality of cooling fluid supplyconnectors, and a fluid conduit connecting the plurality of coolingfluid return connectors to the cooling fluid reservoir to allow flow offluid from the cooling fluid return connectors to the fluid reservoir.The fluid reservoir may conveniently take the form of a standard IV bagfilled with sterile saline solution. Fluid pressure and/or fluid flowsensors may be provided in the cooling fluid circulation system to sensefluid pressure and/or fluid flow to each of the applicators and providefeedback to a pump controller to control the fluid pressure and/or fluidflow to the applicators.

The design of a narrow separation gap between the conductive applicatorinsertion tip and the insertion end of the conductive outer sleeveprovides a zone of high microwave intensity at the gap which can be usedto coagulate tissues along the insertion track if the microwave power isapplied as the microwave antenna is withdrawn from the treated tissue.This provides coagulation of tissue and blood vessels that may be alongthe insertion track as well as any disease tissue that may be along thetrack as the applicator is removed from the tissue. By providingregularly spaced depth markings on the elongate applicator andwithdrawing the applicator from the living body in coordination withregular cadence sounds, a substantially constant rate of removal of theapplicator from a living body can be achieved for effective trackablation. In addition to the regularly spaced depth markings, it hasbeen found advantageous to also provide a warning marking visible on theoutside of the elongate applicator body at a position a known distancetoward the attachment end of the applicator from the portion of theapplicator that creates the tissue ablation (heating zone or zone ofablation). As the applicator is withdrawn from the treated tissue,appearance of this warning marking indicates when the zone of trackablation or coagulation is getting close to the outer skin surface sothat withdrawal of the applicator can be stopped at a desired positionshort of the skin area to avoid damaging or coagulating tissue in theskin area. Further, the fluid injection system can be controlled to stopfluid injection during this track ablation.

THE DRAWINGS

Other features of the invention will become more readily apparent fromthe following detailed description when read in conjunction with thedrawings in which the accompanying drawings show the best modescurrently contemplated for carrying out the invention, and wherein:

FIG. 1 is a side elevation of an applicator, in accordance with anembodiment of the present invention;

FIG. 2 is a vertical section of a portion of the applicator of FIG. 1;

FIG. 3 is a cut away perspective view of a portion of the applicator ofFIG. 2;

FIG. 4 is a vertical sectional of the handle portion of the applicatorof FIG. 1;

FIG. 5 is a circuit diagram of the electrical connections within thehandle portion of the applicator as shown in FIG. 4;

FIG. 6 is a perspective cut away view of another embodiment of handlefor the applicator of the invention;

FIG. 7 is a block diagram of a system for microwave therapy using theapplicator of the invention;

FIG. 8 is a block diagram of a system of the invention for microwavetherapy using an array of applicators of the invention;

FIG. 9 is a side elevation of the applicator shown in FIG. 1, showingadditional depth markings along the applicator;

FIG. 10 is a vertical section similar to that of FIG. 2 of a differentembodiment of applicator of the invention;

FIG. 11 is a schematic representation of a cooling fluid circulationsystem of the invention.

FIG. 12 is computer generated representation of a heating patternproduced by an applicator of the invention wherein the tissue along theproximal portion of the applicator is allowed to dry and char;

FIG. 13 is computer generated representation similar to that of FIG. 12of a heating pattern produced by the same applicator of the invention asused for FIG. 12, wherein fluid is injected into the tissue along theproximal portion of the applicator to limit drying and charring of thattissue;

FIG. 14 is a vertical section similar to that of FIG. 10 of a differentembodiment of applicator of the invention with fluid injection ports;

FIG. 15 is a vertical section similar to that of FIG. 2 of a differentembodiment of applicator of the invention with fluid injection ports;

FIG. 16 is a vertical section similar to that of FIGS. 10 and 14 of adifferent embodiment of applicator of the invention with fluid injectionports and without a cooling fluid return path;

FIG. 17 is a vertical section similar to that of FIGS. 2 and 15 of adifferent embodiment of applicator of the invention with fluid injectionports and without a cooling fluid return path;

FIG. 18 is a schematic representation of a cooling fluid circulationsystem of the invention similar to that of FIG. 11, but without thefluid return line and fluid return connectors, and usable with theapplicators of FIGS. 17 and 18;

FIG. 19 is a schematic representation of a cooling fluid circulationsystem of the invention without the fluid return line, fluid returnconnectors, and fluid pump, and usable with the applicators of FIGS. 17and 18.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

One embodiment of a microwave applicator of the invention for microwavecoagulation and ablation treatment of diseased tissue within living bodytissue is illustrated in FIG. 1. The applicator, referred to generallyas 10, includes a handle 12 from which a substantially rigid elongateapplicator body 14 extends with an insertion tip 16 forming theinsertion end portion of the applicator for insertion into a tissueregion of the living body. The substantially rigid elongate applicatorbody 14 includes an outer conductive sleeve 18 extending from the handle12, a conductive shunt 20, the conductive insertion tip 16, and adielectric collar 22 positioned between the insertion tip 16 and theshunt 20. As can be seen, dielectric collar 22 joins the conductiveinsertion tip 16 to both shunt 20 and through shunt 20 to outerconductive sleeve 18. The outside diameters of the exposed portions ofthe outer conductive sleeve 18, the conductive shunt 20, the dielectriccollar 22, and the insertion tip 16 (which may be sharpened at itsinsertion end 17), are all about equal so as to form a smooth continuouselongate applicator body for insertion into the living body tissue. Theelongate applicator body may be coated with a stick resistant dielectricmaterial such as Teflon, not shown. A pistol grip 24 allows the handleto be easily held for manipulation of the applicator.

The applicator has a microwave antenna portion 25 toward the insertiontip of the elongate applicator body 14 to radiate microwave energy fromthe antenna portion into the living body tissue. Microwave energy istransmitted from the handle 12 through the elongate applicator body tothe antenna portion by a coaxial microwave transmission line 26, FIGS.2-4, within the elongate applicator body and having an inner conductor29 and an outer conductor 27 separated by a dielectric material 28positioned therebetween. Although not required, the coaxial transmissionline 26 may be a semirigid coaxial cable with copper inner and outerconductors and a Teflon or Teflon and air dielectric material. No outerdielectric insulating material is used. Such coaxial cable will usuallyhave about a fifty ohm impedance which provides a good impedance matchto the microwave generator and to typical living body tissuecharacteristics.

The outer diameter of the coaxial transmission line (also the outerdiameter of the outer conductor 27 of the coaxial transmission line) issmaller than the inside diameter of the outer conductive sleeve 18 so aspace 82 is provided between the transmission line and the outerconductive sleeve. This space will be referred to as a cooling fluidspace. Conductive shunt 20 is positioned around and in electricalcontact with both the insertion end portion 83 of the transmission lineouter conductor 27, and the outer conductive sleeve 18. Shunt 20includes a reduced outer diameter end portion 84 toward the handle endof the applicator dimensioned to fit into the space 82 between theoutside surface of the outer conductor 27 of the coaxial transmissionline 26 and the inside surface of the outer conductive sleeve 18. Shunt20 can be soldered to both the outer conductor 27 and the outer sleeve18 to ensure good electrical connection. Soldering will also secureshunt 20 to outer sleeve 18 for a strong connection of shunt 20 tosleeve 18. However, shunt 20 can be secured to sleeve 18 and, ifdesired, to outer conductor 27, by a bonding agent, such as an epoxyadhesive material. If the bonding agent is conductive, it can replacesoldering. With this connection, shunt 20 closes or blocks cooling fluidspace 82 toward the insertion end 85 of the outer conductive sleeve 18.

Shunt 20 extends beyond the actual end 86 of the outer conductor to forman enlarged inside diameter shunt portion 87. The insertion end ofenlarged diameter shunt portion 87 can accept a reduced diametermounting portion 88 of the applicator tip 16 with dielectric collar 22thereon. Dielectric collar 22 fits over the reduced diameter mountingportion 88 of the applicator tip 16, and itself has a reduced diameterinsertion portion 89 that fits into enlarged inside diameter shuntportion 87. This interfitting arrangement produces a strong connectionof the tip to the remainder of the applicator, with the dielectriccollar 22 being bonded to the tip and the shunt by an adhesive materialsuch as epoxy.

Dielectric collar 22, being positioned between shunt 20 and tip 16,electrically insulates tip 16 from shunt 20 and from outer conductivesleeve 18. Since shunt 20 is electrically connected to the outerconductor 27 of the coaxial transmission line 26, shunt 20 becomes anextension of the outer conductor 27 and the insertion end 90 of theconductive shunt 20 becomes the effective insertion end of the outerconductor 27. The inner conductor 29 of the coaxial transmission lineextends toward the insertion end of the applicator beyond the insertionend 91 of the coaxial transmission line dielectric material 28 to aninner conductor insertion end 92. However, both the insertion end 91 ofthe coaxial transmission line dielectric material and the insertion end92 of the coaxial transmission line inner conductor are within theenlarged inside diameter shunt portion 87 of shunt 20 and do not extendbeyond the insertion end 90 of shunt 20.

The reduced diameter mounting portion 88 of applicator tip 16 alsoincludes a tip tab 93 extending therefrom toward the handle end of theapplicator and the insertion end 91 of the coaxial transmission linedielectric 28. The tip tab 93 is positioned so that the extension of thecoaxial transmission line inner conductor 29 beyond the end 91 of thecoaxial transmission line dielectric 28 is adjacent to and can besecured in electrical contact, such as by soldering, to the tip tab 93.With this arrangement, inner conductor 29 does not extend into tip 16,but is merely adjacent to and electrically connected to tip tab 93.

As constructed, the conductive outer sleeve 18 may be of a metalmaterial such as stainless steel, the conductive tip and the shunt maybe formed of a metal material such as brass or stainless steel, and thedielectric insulating collar may be formed of a substantially rigidplastic material. All such parts may be bonded using an epoxy adhesive.Further, while the construction described for this illustratedembodiment provides an embodiment of a microwave antenna toward theinsertion end of the applicator, various other applicator constructionscan be used to form a microwave antenna toward the insertion end of theapplicator and to form an insertion end of the applicator. For example,FIG. 10 shows an alternate embodiment of the insertion portion of theapplicator where the shunt is not used. As shown in FIG. 10, theconductive applicator insertion tip 16 is connected directly to theouter conductive sleeve 18 by dielectric collar 22 which electricallyinsulates the conductive applicator insertion tip from the conductiveouter sleeve 18. Also, the end of dielectric collar 22 toward theattachment end of the applicator extends into the space 82 between theouter conductive sleeve 18 and the outer conductor 27 of the coaxialmicrowave transmission line 26 to electrically insulate the outerconductive sleeve 18 from the outer conductor 27. In this embodiment,the outer conductive sleeve 18 is not electrically connected to theouter conductor 27. Dielectric collar 22 also forms the end toward theinsertion end of the applicator of the cooling fluid space 82. Similarlyto the construction shown in FIG. 2, the insertion tip 16 includes tiptab 93 which is coupled to the inner conductor 29. This construction ofthe antenna and insertion end of the applicator has also been foundsatisfactory for use in the invention.

As shown in FIG. 1, elongate applicator body 14 extends from handle 12.As shown in FIG. 4, outer conductive sleeve 18 is secured in the forwardportion 13 of handle body 15 and in the forward end of cooling fluidreservoir 38, which cooling fluid reservoir 38 is mounted within handlebody 15. Cooling fluid reservoir 38 includes two reservoir chambers 34and 36 separated by guide sleeve 40 that extends from connection toreservoir partition 35 into outer conductive sleeve 18 and within outerconductive sleeve 18 toward the insertion end of the applicator. Theguide sleeve 40 may be a thin walled plastic sleeve made of polyimideplastic such as Kapton. Attachment of the outer conductive sleeve 18 tohandle body 15 and fluid reservoir 38, and attachment of guide sleeve 40to reservoir partition 35, may be with glue, epoxy, or other bondingagent. Coaxial transmission line 26 extends through cooling fluidreservoir 38 and into guide sleeve 40. Coaxial transmission line 26extends through the entire length of guide sleeve 40 and beyond theguide sleeve insertion end 41, FIG. 2, and into shunt 20.

As seen in FIGS. 2 and 4, guide sleeve 40 extends into cooling fluidspace 82 between the outside of coaxial transmission line 26 and theinside of outer conductive sleeve 18. Guide sleeve 40 divides coolingfluid space 82 into an inner cooling fluid space 42 and an outer coolingfluid space 43 along the length of guide sleeve 40 in space 82. Innercooling fluid space 42 is formed between the outside surface of coaxialtransmission line 26 and the inside surface of guide sleeve 40 and outercooling fluid space 43 is formed between the outside surface of guidesleeve 40 and the inside surface of outer conductive sleeve 18.Reservoir chamber 34 communicates with inner cooling fluid space 42 andreservoir chamber 36 communicates with outer cooling fluid space 43.

While either reservoir chamber 34 or 36 could be a cooling fluid inletor cooling fluid outlet, it has been found for ease of placement of thetemperature sensor, as will be explained in respect of the location oftemperature sensor 60, that reservoir chamber 34 can be the coolingfluid inlet reservoir and reservoir chamber 36 can be the cooling fluidoutlet reservoir. In such instance, cooling fluid to the applicator willflow from a source of cooling fluid, not shown, through tubing 30 intoreservoir chamber 34. From reservoir chamber 34, cooling fluid flowsthrough inner cooling fluid space 42 along the outside surface ofcoaxial transmission line 26 to cool the outside surface of coaxialtransmission line 26. As previously indicated in regard to FIG. 2,cooling fluid space 82 into which guide sleeve 40 extends is blocked atthe insertion end portion of outer conductive sleeve 18 by the reduceddiameter portion 84 of shunt 20 which fits into and blocks the insertionend of space 82. As seen in FIG. 2, the insertion end 41 of guide sleeve40 ends before reaching the end of space 82 created by shunt 20 so as toleave an undivided fluid space portion which connects the inner coolingfluid space 42 and the outer cooling fluid space 43. Thus, as coolingfluid flowing in inner cooling fluid space 42 toward the insertion endof the applicator reaches the insertion end 41 of guide sleeve 40, itflows into the undivided space 82 around the insertion end 41 of guidesleeve 40 into outer cooling fluid space 43 and flows along the insidesurface of outer conductive sleeve 18 back into reservoir chamber 36 andout fluid outlet tube 32 back to the fluid supply to be cooled andrecirculated or to a fluid drain.

As shown in FIG. 4, microwave energy is provided to the applicator froma microwave generator, not shown, by a coaxial microwave energy supplycable 46 that provides a path for the microwave energy from thegenerator to the applicator. The coaxial microwave energy supply cable46 is typically a flexible fifty ohm coaxial cable containing an inneror center conductor 48, an outer conductor 49, and a dielectric spacer50 therebetween. In the illustrated embodiment, the connection betweenthe flexible coaxial microwave energy supply cable 46 and the semi-rigidcoaxial transmission line 26 is provided through a coupling circuit on aprinted circuit card 58 which supports small chip capacitors and aresistor, (see also FIG. 5 which is a circuit diagram of the circuitryof FIG. 4). The coaxial microwave energy supply cable center conductor48 is connected by conductive metal path 51 on the circuit card 58 tocapacitor 52 which is connected to inner conductor 29 of coaxialtransmission line 26. The coaxial microwave energy supply cable outerconductor 49 is connected by conductive element or wire 47 to conductivemetal path 53 on the circuit card 58 which is connected to outerconductor 27 of coaxial transmission line 26. This provides a directpath for the microwave currents to flow between the outer conductors.Circuit diagram FIG. 5 shows a capacitor 55 connected between the twoouter conductors 49 and 27 which is not necessary and not shown in FIG.4, but may be advantageous to include to provide further isolation ofthe microwave antenna from dc currents in the flexible coaxial microwaveenergy supply cable 46.

A temperature sensor in the form of a thermistor 60 is placed over theouter conductive sleeve 18 and bonded to it so that it is approximatelythe same temperature as the outer conductive sleeve 18. Thermistor 60,when placed at the location shown in FIG. 4, measures the temperature ofouter conductive sleeve 18 at about its handle end, which will be atapproximately the temperature of the cooling fluid after flowing throughthe elongate applicator body 14. Thermistor 60 can be located at otherlocations that enable it to indicate the approximate temperature of thecooling fluid after or during flow through the applicator. When locatedas shown, thermistor 60 measures the approximate temperature of thecooling fluid between guide sleeve 40 and the outer conductive sleeve 18as the cooling fluid returns to the cooling fluid outlet reservoirchamber 36 after flowing through inner and outer cooling fluid spaces 42and 43. The cooling fluid at this location will have reachedapproximately its highest temperature. Thermistor 60 could be located inthe cooling fluid itself, if desired, such as in cooling fluid outletreservoir chamber 36. The function of this thermistor 60 is to providean indication that the cooling fluid is actually flowing inside theapplicator whenever the microwave power is applied. During theapplication of microwave energy, the microwave energy causes selfheating of the coaxial transmission line 26 in the applicator. Thisincreases the temperature of coaxial transmission line 26 therebyheating the surrounding parts between thermistor 60 and coaxialtransmission line 26. Without circulation of cooling fluid, applicatorouter conductive sleeve 18 can reach temperatures that can damage normaltissue. The flow of cooling fluid inside the applicator along coaxialtransmission line 26 and outer conductive sleeve 18 removes much of thatgenerated heat so that thermistor 60 remain cooler when the coolingfluid is flowing than if there is no fluid flow. If fluid flow stops oris restricted, the fluid will heat to a higher temperature than whenproperly flowing. When properly flowing, the applicator outer conductivesleeve 18 will remain below tissue damaging temperatures.

A thermistor is a resistive electrical device that varies its resistancedepending upon its temperature. The two wires 62 a and 62 b fromthermistor 60 are connected across capacitor 56. Wire 62 a connects tocapacitor 56 and also connects directly to outer conductor 49 of theflexible coaxial cable 46. Wire 62 b attaches to the opposite side ofcapacitor 56 and also to one side of resistor 54 through conductivemetal path 57. The other side of resistor 54 connects to conductivemetal path 51 via a wire or conductive metal path 59. Thus, thermistor60 is connected electrically between inner conductor 48 and outerconductor 49 of flexible coaxial cable 46. This enables the resistanceof the thermistor 60 to be monitored by a direct electrical current thatis passed from the center conductor 48 through conductive metal traces51 and 59 to resistor 54 and conductive metal trace 57 and wire 62 b tothermistor 60 and back via wire 62 a and wire 47 to the outer conductor49 of flexible coaxial cable 46. Capacitor 52 prevents the directelectrical current from flowing into inner conductor 29 of coaxialtransmission line 26 and therefore prevents the direct electricalcurrent from flowing into the applicator antenna and living body intowhich the applicator is inserted. If capacitor 55 is provided in thecircuit, it prevents the direct electrical current from flowing into theouter conductor 27 of coaxial transmission line 26 to further ensurethat direct electrical current does not flow into the antenna and intothe living body into which the applicator is inserted. This describedcircuitry allows the flexible coaxial microwave energy supply cable toserve a dual purpose. The dc current for monitoring of the resistance ofthermistor 60 passes through the flexible coaxial microwave energysupply cable 46 along with the microwave energy that flows through theflexible coaxial microwave energy supply cable 46 from the microwaveenergy generator to the applicator. With the arrangement described, thetemperature indicating signal is carried between the thermistor and thesystem controller over the same two coaxial cable conductors 48 and 49that carry the microwave power from the microwave generator to theapplicator. This eliminates the need for separate additional wires fromthe handle to the system controller to carry the temperature signalsfrom the thermistor.

As indicated, the signal from the thermistor 60 provides an indicationto the system controller of the temperature of the outer conductivesleeve and the cooling fluid circulating in the applicator. With themicrowave power applied to the applicator, which results in heating ofcoaxial transmission line 26, as long as cooling fluid is properlyflowing in the applicator, the temperature of thermistor 60 will remainlow. If the cooling fluid stops flowing in the applicator or flow isrestricted for some reason, the coaxial transmission line 26 will beginto heat and the temperature of outer conductive sleeve 18 and of anynon-flowing or slowly flowing fluid in the applicator will alsoincrease. This increases the temperature of thermistor 60. This increasein measured temperature of thermistor 60 provides an indication thatcooling fluid is not flowing properly and the system controller canactivate an alarm or activate other corrective action.

FIG. 6 shows a cut away perspective view of a handle similar to that ofFIG. 4, but with a slightly different configuration of handle body 45and different orientation of inlet 30 and outlet 32 tubes from reservoirchambers 34 and 36. However, the configuration of the handle componentsis substantially the same and components are numbered the same as inFIG. 4. The wires from the thermistor 60 are not shown. FIG. 6 gives abetter illustration of the actual construction of the applicator handle.

As can be appreciated from the above explanation, in addition toproviding a means by which the applicator can be held and manipulatedfor insertion into the living body, handle 12 serves as an interfacebetween the substantial rigid elongate applicator body 14 and theflexible coaxial microwave energy supply cable extending from themicrowave generator to the applicator, provides for the insertion of thetemperature signals onto the flexible coaxial microwave energy supplycable, and serves as an interface between the flexible fluid hoses fromand to a source of cooling fluid and the cooling fluid reservoirs.Various configurations of handles can be used. While the flexiblecoaxial microwave energy supply cable and the flexible fluid hoses areshown extending from the end of the handle grip (and could be enclosedin a sheath, if desired), connectors could be provided directly on thehandle so that the flexible coaxial microwave energy supply cable couldbe connected to and disconnected from the handle and so that theflexible fluid hoses could also be connected to and disconnected fromthe handle. In the embodiment shown in FIG. 4, the flexible coaxialmicrowave energy supply cable 46 and the flexible fluid hoses 30 and 32are shown coming together in side-by-side relationship in the handle 12and entering a sheath 154 which extends out of the end of the pistolgrip 24 to keep the cable and hoses together for a distance extendingfrom the handle. This allows easier maneuvering of the applicator duringuse. The hoses 30 and 32 and cable 46 extend from the end 156 of thesheath 154 and the hoses terminate in hose connectors 158 and 160adapted for connection to a cooling fluid supply hose connector and acooling fluid return hose connector. Coaxial cable 46 terminates in acable connector 162 adapted to connect to a further microwave energysupply cable. Various materials can be used for the sheath 154. Aplastic braid material that functions like the old “Chinese Handcuff” totighten around the enclosed cable and hoses has been found satisfactoryto provide a good outer covering to improve the handling and storage ofthe applicator, and to allow heat generated by the coaxial cable toeasily pass through it.

FIG. 7 is a functional block diagram of a basic system of the inventionas described above using a single applicator for patient treatment. Anoperator interface 61, such as a computer screen and keyboard or asimple touch screen, is provided for display and monitoring of thesystem controls and the treatment procedures. The user interface isconnected to a system controller 64, such as a computer processor, by acable 63. The controller provides control and monitoring to a microwavegenerator 68 through a cable 66. The generator 68 has a microwaveoscillator where the power amplitude can be controlled and monitored bythe controller 64 including the measurement of both the forward andreflected power at the output of the generator 68. The generatedmicrowave power is then directed to a multiplexer and power splittercircuit 74 by a transmission line cable 70, such as a coaxial cable. Themicrowave path inside the multiplexer and power splitter circuit 74contains an impedance matched microwave path directing the microwavepower to the applicator 10 with elongate applicator body 14 by aflexible coaxial microwave energy supply cable 72. As described, withinthe applicator 10 there is a dc current path that flows through atemperature sensing thermistor that enables a direct current to alsoflow through the coaxial microwave energy supply cable 72. This directcurrent that is used to measure the temperature within the applicatorelongate body 14 is separated from the microwave power signal in themultiplexer portion of the multiplexer and power splitter circuit 74 andis sent along a dc circuit path 76 that is directed to a temperaturemonitoring circuit 78. The temperature monitoring circuit 78 thendirects a temperature signal back to the controller 64 through a cable80 to enable the controller to monitor and control microwave powerlevels generated by microwave generator 68 to limit the microwave powertransmitted to the applicator if excessive temperatures are measured inthe applicator 10. Temperature monitoring circuit 78 may be part of thecontroller 64.

In many instances, it will be desired to provide patient treatment usinga phased array of applicators rather than a single applicator. Whenusing a phased array, a plurality of applicators are inserted into thepatient in approximately parallel orientation in a pattern approximatelyevenly spaced apart along the circumference of an insertion circlearound the tissue to be treated. Each applicator should be inserted sothat the radiating antenna is at approximately the same depth positionwith respect to the tissue to be treated so as to have the radiationfeedpoints approximately aligned side by side. The use of multipleapplicators in phased arrays generally allows better control of theapplicators to produce better uniformity of power deposition,temperature, and/or coagulation of tissue throughout a tumor volume tobe treated and particularly at the tumor margins than when using asingle applicator. The use of phased arrays can also reduce microwaveheating along the shafts of the applicators due to cross coupling of theenergy between the antennas that are driven in phase and separated by adistance that provides for partial power cancellation along the outerportion of the inserted applicators and an increase in tissue heatingbetween these inserted applicators. With phased arrays, pretreatmentplanning can be used to provide an ideal insertion pattern and power andphase application to the array of applicators to produce and control thedesired heating. The treatment is thereby optimized and controlled bythe aid of a numerical calculation of either the planned insertionpattern and number of antennas or the actual pattern achieved asindicated by various non-invasive imaging processes such as computertomography (CT), ultrasound, or magnetic resonance imaging (MRI). Poweramplitude and phase of each of the inserted applicators can be adjustedas directed by a computer-controlled system using the predicted powerpatterns from the computer numerical model. Further, actual temperaturemeasurements can be taken and compared with the predicted power patternsand predicted temperatures and the system controlled to compensate fordifferences.

In a phased array embodiment of the invention, a single microwavegenerator is used to provide the microwave power for all applicators.The generator will usually operate at 915 MHz, which is an emissionfrequency commonly licensed for medical applications. This singlegenerator is connected to a passive, non-switching, microwave impedancematched power splitter (divider) which is used to direct powersimultaneously to multiple ports that are connected to one or moremicrowave dipole antenna such as described for the above describedapplicators. This arrangement provides approximately equal powersimultaneously to each of the output connection ports. This arrangementalso provides equal phase output of the microwave energy at each of theoutput ports. Thus, when multiple antennas are connected to the ports ofthe power splitter, they have equal power and equal relative phase andare thus correctly called a phased array of antennas. The cables goingto the radiating points on each antenna are maintained at the sameelectrical length so that the radiated energy from the antennas arephase synchronous and phase coherent. Phase synchronous meaning thatthere is a fixed phase relationship between the radiation phase of allantennas and phase coherent meaning that the relative radiated phasefrom each antenna is approximately the same. Since different arraypatterns are desirable for different optimized treatments, and desiredtreatments can use a single applicator or varying numbers of multipleapplicators, it is desirable to have a system which can power andmonitor a single applicator or a multiple number of applicators.However, present systems are usually designed to optimize power deliveryto either a single applicator or to a set number of multipleapplicators. This does not provide the flexibility desired to configuredifferent arrays using a single delivery system. It would also bedesirable in array power systems to have an indication as to whether ornot there is an antenna connected to a particular microwave power outputport and an indication as to whether antennas are correctly connected.

FIG. 8 shows an embodiment of a multiplexer and power splitter circuitaccording to the invention that provides for the separation oftemperature signals from microwave power signals for a plurality ofapplicators and which can provide optimization for attachment of asingle applicator, two applicators, or three applicators. Microwavepower signals from a microwave generator, not shown, are supplied to themultiplexer and power splitter circuit through coaxial cable 100,generally of fifty ohm impedance. The multiplexer and power splittercircuit is generally on a printed circuit card made of low lossdielectric material such as Teflon based material with a ground plane onone side and the circuit show in FIG. 8 that represents the conductivepaths forming various transmission lines on the other side. The inputmicrowave power signal connects to an input in the form of a conductivepatch 102 that provides a power splitting section. This directsmicrowave power to four paths, one path shown by path 104, and threeidentical paths shown by paths 114. Along path 104 is a chip typecapacitor 106 that conducts microwave power but blocks direct current toprevent direct current from reaching power splitting patch 102. Theinput microwave power flows through capacitor 106 to circuit output port110 along transmission line 108. The transmission lines 104 and 108 arefifty ohm transmission lines which together have an electrical lengthdelay of one hundred eighty degrees at the microwave operatingfrequency. Capacitor 106 has a low impedance of typically less than twoohms reactive impedance to avoid mismatching the transmission line. Thisthen directs microwave power from the input transmission line 100 to thecircuit output port 110. Output port 110 forms an output port forconnection of a single applicator antenna through a fifty ohm impedancecoaxial microwave energy supply cable attached to output port 110. Thisoutput port 110 is used if only a single antenna is to be connected tothe multiplexer and power splitter circuit, and is sometimes referred toherein as a single connection output port.

Power splitter conductive patch 102 is also connected to three identicalother transmission lines having microwave input sections 114 each with aseries chip capacitor 112 along the path, and microwave output sections116. Similarly to capacitor 106, each capacitor 112 in the microwaveinput section has a low impedance of typically less than two ohmsreactive impedance to allow microwave power to pass but block directcurrent flow to prevent direct current from reaching power splittingpatch 102. The overall length of the microwave input section of thetransmission lines from the power splitter conductive patch 102 throughthe capacitor 112 along path 114 is approximately ninety degrees delayat the microwave frequency. Also the characteristic impedance of themicrowave input section of the transmission lines 114 with capacitors112 of typically between seventy and ninety ohms from the power splitterconductive patch 102 to the end of path 114 is used to provide animpedance matching section for the input when two or three applicatorsare connected to the multiple connection output ports 118. The microwaveoutput sections 116 are fifty ohm sections that connect the lines 114 tothe multiple connection output ports 118 and these microwave outputsections 116 are typically the length to delay the microwave signalapproximately ninety degree. The fifty ohm impedance of the microwaveoutput sections 116 provide impedance matching for the flexible coaxialmicrowave energy supply cables and the applicators connected to theoutput ports 118.

The described power splitter circuit forms an impedance matchedmicrowave power splitter that when a single applicator is to be used italone is connected to the single connection output to port 110. Whenthis is the case the other three output ports, each a multipleconnection output port 118, are not connected to an applicator. The pathlength from the power splitter conductive patch 102 to each of thesemultiple connection output ports 118 is one hundred eighty degrees. Themicrowave power that travels to these multiple connection output ports118 is reflected completely back when there is no connection to theports and this reflected power is reflected with the same phase angle asthe incoming power to these ports because this is an open circuittermination. This means that the overall phase delay of the power fromthe power splitter conductive patch 102 to the multiple connectionoutput ports 118 and back to the power splitter conductive patch 102 isthree-hundred-sixty degrees. This unique phase delay then appears to thepower splitter as an open circuit. Thus, the open ports 118 turn thesepaths into tuning paths that do not reflect power that would reach theinput line 100, but would direct the full power only to singleconnection output port 110 to the single applicator that is connected tooutput port 110 for efficient power transfer to the single applicator.

When two or three applicators are connected to respective multipleconnection output ports 118, there will be no applicator connected tothe port 110. The path delay between the power splitter conductive patch102 and the output port 110 is also one-hundred-eighty degrees.Therefore, the delay to the output port 110 and back to the conductivepatch 102 is three-hundred-sixty degrees. When there is no applicatorattached to the single connection output port 110 it also turns into atuning path for the microwave energy. The result is that the microwavemultiplexer and power splitter circuit is an impedance matched splitterwhich automatically allows the power to be directed to the connection of1, 2, or 3 applicators. It would not be permitted to attach only asingle applicator to one of the multiple connection output ports 118because it would result in an impedance mismatch and would causeunacceptable reflected power to the input line 100. Also, if noapplicators are connected to any of the ports of the power splittercircuit, all transmission paths appear as open circuits. This allowsmultiple power splitter circuits to be use to provide for more thanthree applicators when desired. For example, if two power splittercircuits are used anywhere between one and six applicators can beconnected to the system.

The multiplexer and power splitter circuit also includes an inductivecoil or choke 120, 122, 124, and 126 connected to each of thetransmission lines 104 and 114. Each of these inductive coils isconnected through a capacitance to the ground chassis with capacitors128, 130, 132, and 134, respectively. These capacitors and the inductivecoils filter the microwave signals from the temperature sensing ports136, 138, 140, and 142, but pass direct current signals from thetransmission lines 108 and 114 to these temperature sensing ports. Thesetemperature sensing ports are connected to temperature monitoringcircuitry and then to the system computer or controller for detection ofthe measured resistance of the thermistors that are connected to the twowire coaxial microwave energy supply connectors of the applicators aspreviously described. These direct current temperature sensing signalsfrom the applicators to the temperature sensing ports provide ameasurement to the system controller of the temperature measured by thetemperature sensors in each of the applicators.

These direct current temperature sensing signals from the applicators tothe temperature sensing ports also provide a measurement to the systemcontroller of whether applicators are connected to particular outputports of the multiplexer and power splitter circuit. If an applicator isconnected to a particular multiplexer and power splitter circuit outputport, for example to output port 110, a temperature signal will bepresent on temperature sensing port 136. The system controller will thenknow that an applicator is connected to output port 110. Similarly, if atemperature signal is present on temperature sensing ports 138 and 142,the system controller will know that two applicators are connected totwo of the multiple connection output ports 118 and will be able toidentify which of the two output ports have applicators connectedthereto. If the system controller senses temperature signals ontemperature sensing ports 136 and 138, the system controller knows thatthere are two applicators connected to the multiplexer and powersplitter circuit, but that the applicators are not properly connectedsince one of the two applicators is improperly connected to singleconnection output port 110 while the other of the two applicators isproperly connected to one of the multiple connection output port 118.The system controller can then provide a warning signal to a system userindicating that the applicators are improperly connected, and that theapplicator connected to the single connection output port 110 should bedisconnected and connected to one of the multiple connection outputports 118. The use of this special multiplexer and power splittercircuit, in addition to providing an indication that the proper numberof applicators are connected to the correct output ports for efficientand desired microwave power delivery to the connected applicators, alsoenables the measurement of applicator cooling temperature to determinethat fluid is properly flowing in each of the connected applicators toprotect the normal body tissues.

If temperature sensing is not required, but the sensing of theattachment of microwave applicators to power splitter circuits isdesired, the thermistor or other temperature sensors that provide directcurrent temperature signals can be replaced with regular resistors whichwill provide substantially dc signals in the manner of thermistor toindicate that microwave applicators are attached to a power splitteroutput port and indicate to which port or ports the applicators areattached. This use of resistors will be considered equivalents of thethermistors or other temperature sensors that provide direct currenttemperature sensor signals for the purposes of the applicator detection.

Another consideration when using arrays of multiple fluid cooledapplicators in which cooling fluid is circulated through theapplicators, is the necessity to provide a source of cooling fluid and areturn line for cooling fluid for each of the applicators. In order tomake connection of a variable number of applicators quick and easy, theinvention can provide a cooling fluid circulation system adapted toconnect to and provide cooling fluid circulation for a single applicatorup to a preset number of multiple applicators. Referring to FIG. 11, acooling fluid circulation system of the invention includes a pluralityof cooling fluid supply connectors 166, (here shown as three connectors)each adapted to be connected to an applicator cooling fluid inlet, suchas a cooling fluid inlet connector 158 of FIG. 4. An equal plurality(here three) of cooling fluid return connectors 168 are provided eachadapted to be connected to a cooling fluid outlet, such as a coolingfluid outlet connectors 160 of FIG. 4. Each of the plurality of coolingfluid supply connectors 166 includes a normally closed shut off valvewhich opens when connected to an applicator cooling fluid inlet. Thisshut off valve prevents flow of fluid from the cooling fluid supplyconnector except when connected to a cooling fluid inlet. Each of theplurality of cooling fluid return connectors 168 includes a one way flowvalve allowing flow of fluid only into a cooling fluid return connector.This prevents fluid flow out of the system through a cooling fluidreturn connector 168, but will allow return fluid to flow into thesystem through such connector when connected to an applicator coolingfluid outlet 160. The cooling fluid supply connectors 166 are configuredto connect to the cooling fluid inlet connectors 158, but not to thecooling fluid outlet connectors 160. Similarly, the cooling fluid returnconnectors 168 are configured to connect to the cooling fluid outletconnectors 160, but not to the cooling fluid inlet connectors 158. Inthis way, a user cannot improperly connect the cooling fluidconnections.

In the system of FIG. 11, a cooling fluid pump 170 draws cooling fluidthrough line 172 from a cooling fluid reservoir 174 and pumps it throughline 176 and line splitter 178 into lines 180 to the plurality ofcooling fluid supply connectors 166. Each of the cooling fluid returnconnectors 168 is connected to a line 182 connecting to a line joiner184 connected through line 186 to the cooling fluid reservoir 174. Thus,cooling fluid is pumped from the reservoir to the plurality of coolingfluid supply connectors 166. Cooling fluid from an applicator is allowedto flow from the cooling fluid return connectors 168 back to the fluidreservoir 174. The fluid reservoir 174 may conveniently take the form ofa standard IV bag filled with sterile saline solution. This providessterile saline solution as the cooling fluid.

With the illustrated cooling fluid circulation system of the invention,when only a single applicator is used, one of the plurality of coolingfluid supply connectors 166 is connected to the cooling fluid inlet 158of the single applicator and one of the plurality of cooling fluidreturn connectors 168 is connected to the cooling fluid outlet 160 ofthe single applicator. This will provide flow of cooling fluid throughthe single applicator. No cooling fluid will flow through any of thecooling fluid supply connectors or the cooling fluid return connectorsthat are not connected to the applicator. When a plurality ofapplicators is used, a separate one of the plurality of cooling fluidsupply connectors 166 is connected to the cooling fluid inlet 158 ofeach of the plurality of applicators, and a separate one of theplurality of cooling fluid return connectors 168 is connected to thecooling fluid outlet 160 of each of the plurality of applicators. Thiswill provide a cooling fluid supply connector 166 connected to each ofthe applicator cooling fluid inlets 158 and a cooling fluid returnconnector 168 connected to each of the applicator cooling fluid outlets160 and thereby provide a flow of cooling fluid through each of theplurality of applicators attached to the system. Any number ofapplicators up to the number of cooling fluid supply connectors in thefluid supply system, here shown as three, can be connected to the fluidsupply system. Again, no cooling fluid will flow through any of thecooling fluid supply connectors or the cooling fluid return connectorsthat are not connected to an applicator. This makes a fluid supplysystem that is very simple and easy to clinically use. The operatorsimply connects the mating fittings from the antenna to the matchingtype of connectors on the cooling fluid circulation system. The inputand output have different type of connector fittings to avoid mistakes.The operator only need to connect the number of antennas that are to beused and the other unused fittings remain blocked to prevent loss ofcooling fluid. The operator is not required to remove and discard anycomponents or add components, but only to connect things together. Thedesign also enables storage and sterilization of a cooling fluidcirculation system that is made to fit all their applications providingmuch simplification in clinical utilization. The standard IV bags thatform the fluid reservoir can be obtained already filled with sterilesaline. The whole cooling fluid circulation system and fluid reservoiris delivered sterilized for use in surgical and interventional invasiveprocedures.

In many cases, it is desirable to keep the microwave power on to theapplicator as the applicator is withdrawn from the treatment site in thebody when treatment of the diseased tissue is completed. This isbecause, in some instances, diseased tissue from the treatment site maybe left along the insertion and withdrawal track which can seedadditional diseased tissue growth. Further, in many body locations,removal of the applicator leaves an open wound along the insertion trackwhich will bleed. Application of heat as the applicator is withdrawnprovides coagulation of tissue and blood vessels that may preventbleeding along the insertion track during withdrawal of the applicatorfrom the treatment site. As shown in FIG. 9, a narrow separation gap 22between the conductive applicator insertion tip 16 and the effectiveinsertion end of the outer conductive sleeve 18, which is the insertionend of the shunt 20, provides a zone of high microwave intensity at thegap which can be effectively used to coagulate tissues along theinsertion track if the microwave power is applied as the microwaveantenna is withdrawn from the treated tissue. While methods of stepwisetrack ablation are known where the applicator is withdrawn in steps withmicrowave ablation heating performed at each step, and while it is knownthat track ablation can be performed with a continuous withdrawal of theapplicator, effective continuous track ablation requires a substantiallycontrolled constant preset withdrawal rate for the applicator. This isdifficult to obtain when withdrawing an applicator.

As shown in FIG. 9, the applicator of the invention can be provided withdepth marking 150 visible on the outside of the elongate applicator bodyat regular intervals along the elongate applicator body. The purpose ofthese markings is to provide an indication as to the depth of applicatorpenetration into the living body, and such markings are regularlyspaced, such as every centimeter, along a portion of the length of theelongate applicator body where marks can be used to indicate depth ofpenetration. It has been found that these regularly spaced depthmarkings along the inserted shaft can be used to guide the rate ofwithdrawal of an applicator to provide effective coagulation of theinsertion track. For this process, the system includes a sound generatorthat can generate a regular cadence sound. The sound generator may, forexample, be part of the controller. By coordinating the cadence soundswith the amount of withdrawal of the applicator as indicated by thedepth markings that appear as the applicator is withdrawn, the propersteady rate of withdrawal of the applicator can be obtained to assureuniform coagulation of tissues along inserted track. A typical desiredrate of withdrawal of an applicator of the invention is approximatelyfive mm per second at a sixty watt power level. So, for example, if thedepth markings are spaced one cm apart along the inserted shaft, with acadence that provides an audible signal, such as a beep, every second,the cadence sound provides a guide for the withdrawal at a rate of fivemm for each audible beeping sound. This provides a rate of one cm everytwo seconds (every two beeps) to assure uniform coagulation of tissuesduring the withdrawal to reduce bleeding along the inserted track. Thismeans that the applicator is withdrawn so that a depth mark appearsevery two beeps.

In addition to the regularly spaced depth markings, it has been foundadvantageous to also provide a warning marking 152, such as a red orother color marking, visible on the outside of the elongate applicatorbody at a position a known distance toward the attachment end of theapplicator from the portion of the applicator that creates the tissueablation (heating zone or zone of ablation). This distance, for example,could be about two to three cm from the attachment end of the heatingzone (with the applicator shown, this will be about five cm from theinsertion end of the applicator). As the applicator is withdrawn fromthe treated tissue, appearance of this warning marking indicates thatthe zone of tract ablation or coagulation is getting close to the outerskin surface (about two or three cm) so that withdrawal of theapplicator can be stopped at a desired position short of the skin areato avoid damaging or coagulating tissue in the skin area. The physicianwithdrawing the applicator to perform track ablation is thus alerted tothe closeness to the skin surface and can either stop the tract ablationat that time or only continue tract ablation for a short additionaldistance whichever, in the best judgment of the physician, will bothprovide adequate tract coagulation and also protect the skin surface.

While it is generally considered important to avoid or lessen as much aspossible the sticking of tissue, such as heated coagulated or ablatedtissue, to the applicator, it has been found that some sticking may beadvantageous for fixing the position of the applicator in the tissue tobe treated for the duration of the treatment. In an embodiment of theinvention, the dielectric collar 22, such as shown in FIGS. 1, 2, 9, and10, is left uncovered by material, such as a Teflon coating, thatotherwise would cover the dielectric collar 22 to reduce tissuesticking, and the dielectric material is a material, such as PEEK(polyetheretherketone), that heated tissue will stick to. This is arelatively small area along the applicator, but upon heating, the tissuewill stick to this dielectric material. This has the beneficial effectto secure the applicator to the tissue through the ablation procedure.This sticking occurs in about the first minute of the treatment periodand helps to provide a secured positioning of the antenna relative tothe target tissue so that the antenna stays in the intended locationduring the remainder of the treatment period which typically can be nineminutes or more. The PEEK material is a very high temperaturethermoplastic with excellent chemical resistance. It has excellentmechanical properties with high flexural strength, impact resistance,tensile strength, is substantially rigid, and bonds well with epoxy.When removal of the applicator is desired (with the sticking there is aresistance to directly pulling the applicator straight out of thetreated tissue, and such straight out removal is not recommended), theapplicator can be rotated, such as through between thirty and forty-fivedegrees of rotation, which easily releases the sticking tissue to permitremoval of the applicator.

A limitation found in current microwave applicators that are used formicrowave coagulation and ablation is that the energy distributionpattern generally extends back along the applicator from the proximalend of the desired coagulation and ablation zone around the microwaveenergy radiating portion of the applicator toward the proximal end ofthe applicator. This undesirably extends the coagulation and ablationzone along the applicator toward the proximal end of the applicatorbeyond the tissue desired to be coagulated or ablated, and forms what isreferred to as a tail. This results in an elliptical or tear drop shapedenergy distribution and heating pattern shape with a similarly shapedcoagulation and ablation zone where the generally desired shape for theenergy distribution pattern and the coagulation and ablation zone isgenerally more spherical. The inventors have theorized that this tail orextension of the heating pattern along the proximal portion of theapplicator may be due, at least in part, to the drying of the tissuesurrounding this proximal portion of the applicator as a result of theheating of the tissue, and that if the drying of the tissue can bereduced, the heated tail formed would also be reduced. As tissue isheated, moisture is driven from the tissue by the heat and the tissuedries. As the tissue dries, the dielectric constant of the tissuedecreases and the heating of the tissue increases, further drying andeventually charring the tissue. While this heating and charring of thetissue is not a problem in the desired ablation zone since this ablatesthe tissue desired to be ablated, it is a problem when it extends theablation zone into tissue not desired to be ablated. An example of thiselongation of the heating zone which produces the heated tail is shownin FIG. 12. FIG. 12 is a numerical model created by the COMSOL computermodeling program of an expected heating pattern produced by a microwaveapplicator represented by cylinder 200 with a microwave radiating anddesired heating zone 25 at the distal portion 202 of the applicator.Area 204 represents the dielectric collar, such as collar 22 in FIGS. 1,2, and 10, and area 206 represents the conductive insertion tip 16 inFIGS. 1, 2, and 10. The heating pattern shown assumes overheating anddrying to the point of charring of the tissue along the entire insertedlength of the applicator represented by cylinder 210 surroundingapplicator 200. The tissue dielectric is assumed constant at livertissue values under normal conditions of ∈=46.7 and σ=0.86 S/m with thesurrounding cylinder 210 representing dried charred tissue at charredtissue values of ∈=5.2 and σ=0.13 S/m. The proximal end of theapplicator is at the top of FIG. 12 showing the extension of the heatingzone extending toward the proximal end of the applicator and showing theteardrop shape of the heating zone.

FIG. 13 is a numerical model created by the COMSOL computer modelingprogram of an expected heating pattern produced by the same microwaveapplicator represented by cylinder 200 with a microwave radiating anddesired heating zone 25 at the distal portion 202 of the applicator.This heating pattern assumes overheating and drying to the point ofcharring of only the tissue along the desired heating zone representedby cylinder 212 (modeled as four centimeters in length) which extendsjust beyond each end of the microwave radiating zone 25 at the distalportion 202 of the applicator. This represents the situation where thetissue extending from the proximal end 214 of the desired heating zone212 toward the proximal end of the applicator at the top of FIG. 13,referred to sometimes herein as the proximal tissue, remains moist andis not dried. Again, the tissue dielectric is assumed constant at livertissue values under normal conditions of ∈=46.7 and σ=0.86 S/m with thesurrounding cylinder 212 representing dried charred tissue at charredtissue values of ∈=5.2 and σ=0.13 S/m.

A comparison of FIGS. 12 and 13, shows the heating pattern in FIG. 13where the proximal tissue remains moist is shorter and more spherical inshape with much less of a tail toward the proximal end of the applicatorthan the heating pattern of FIG. 12 in which the proximal tissue driesout. In the models, the contour line 216 representing a calculated modeltemperature of about 340 degrees K in FIG. 12 is 6.6 cm compared to 6.1cm in FIG. 13, and contour line 218 representing a calculated modeltemperature of about 328 degrees K in FIG. 12 is 8.1 cm compared to 6.8cm in FIG. 13. These Figs. support the inventors' theory that theelongation of the heating pattern is in part due to the heating anddrying of the proximal tissue. Therefore, if the proximal tissue is kepthydrated during treatment, the heating pattern produced is a moredesirable spherical heating pattern than the heating pattern producedwhen the tissue is not kept hydrated.

FIG. 14 is a vertical section of the applicator of FIG. 10 additionallyincluding one or more small openings, holes, or slots 190 extendingthrough the outer conductive sleeve 18 which allow a portion of thefluid circulating in the cooling fluid space 82 of applicator 14 to flowthrough outer conductive sleeve 18 of applicator 14 and be injected intothe tissue surrounding the outer conductive sleeve in the area of theopenings 190. The openings 190 are positioned to inject cooling fluidinto the tissue in a region of the tissue starting at approximately theproximal end of the desired heating area 25 (the end of the desiredheating area or primary energy radiation zone toward the attachment orproximal end of the applicator) and extending a distance toward theattachment or proximal end of the applicator represented by the handlein FIG. 1. The distance along the applicator from the proximal end ofthe desired heating area 25 toward the proximal end of the applicatorthat fluid injection extends and the number of openings and arrangementof the openings around the conductive outer sleeve 18 is a distance,number, and arrangement determined to be effective to reduce or limitdrying of the tissue and reduce or limit the extent of the elongation ofthe heating pattern a desired amount compared to the elongation of theheating pattern produced by the particular applicator under similaroperating conditions without the injection of the fluid. This hydratedtissue will be referred to as the proximal tissue adjacent the desiredheating zone. The purpose of injecting a portion of the cooling fluidcirculating in the applicator into the tissue is not to directly coolthe proximal tissue adjacent the desired heating zone with the fluid,but to hydrate or wet the proximal tissue adjacent the desired heatingzone so it does not dry. This hydrating of the proximal tissuecounteracts the drying of the tissue that would otherwise occur andtends to maintain the normal dielectric constant of this proximaltissue. This reduces the amount of microwave energy that travels downthe proximal portion of the applicator, which in FIG. 14, reduces theamount of microwave energy that travels from the desired heating zonedown outer conductive sleeve 18.

FIG. 15 is a vertical section of the applicator of FIG. 2, whichincludes the conductive shunt 20 between the dielectric collar 22 andthe outer conductive sleeve 18, and additionally includes the one ormore small openings, holes, or slots 190 extending through the outerconductive sleeve 18 as shown in FIG. 14, which allow a portion of thefluid circulating in the cooling fluid space 82 of applicator 14 to flowthrough outer conductive sleeve 18 of applicator 14 and be injected intothe proximal tissue adjacent the desired heating zone. While thearrangement of the openings extending through the outer conductivesleeve 18 are spaced a short distance from the immediate proximal end ofthe desired heating zone 25, this is still considered for purposes ofthe invention to be at the approximate proximal end of the desiredheating zone. Further, usually the fluid injected into the tissue willspread some from the openings toward the immediate proximal end of thedesired heating zone 25. While the short distance shown from theimmediate proximal end of the desired heating zone 25 may allow theheating zone to expand a short distance toward the proximal end of theapplicator, this short distance generally will not be significant. Ifdesired, the reduced outer diameter end portion 84 of shunt 20 could beshortened to allow openings through the outer conductive sleeve 18 to bepositioned closer to the immediate proximal end of the desired heatingzone 25 or passages could be provided in the reduced outer diameter endportion 84 of shunt 20 leading to openings through outer conductivesleeve 18 closer to the immediate proximal end of the desired heatingzone 25.

The embodiments of FIGS. 14 and 15 maintain the circulation of thecooling fluid into and out of the applicator and through the applicatorcooling fluid space 82, however there will be less fluid flowing fromthe applicator through the fluid return than is supplied the applicator.A fluid circulation system such as shown in FIG. 11 can be used tosupply the cooling fluid to the applicator and receive the return flowof cooling fluid from the applicator. In such instance, fluid pump 170will generally provide sufficient hydraulic pressure to force a smallamount of fluid through the openings 190 in the outer conductive sleeve18 into the tissue to keep the proximal tissue adjacent the desiredheating zone hydrated. The typical flow rate of cooling fluid in thecooling fluid space within the illustrated applicator body is in therange of 20 to 40 ml/minute. The rate needed to infuse fluid into thetissue in the inserted proximal portion of the applicator is generallyless than 10 ml/minute and typically in the range of 1 to 6 ml/minute.Pump 170 in the fluid circulation system of FIG. 11 can generally bechosen to provide ample flow to the number of applicators connected tothe fluid circulation system to permit the small volume to pass into thetissue while maintaining cooling circulation through the applicator. Ifdesired or necessary, particularly when a large variable number ofapplicators can be attached to the fluid circulation system, such asmore than the three possible with the system shown, pressure and/or flowsensors and a pump controller can be provide to measure and maintain thepressure and/or flow rate of the fluid supplied to connected applicatorssufficient to ensure desired fluid injection to the proximal tissueadjacent the desired heating zone through the connected applicators whena large number of applicators are connected to the fluid circulationsystem without providing too much pressure and fluid injection when onlyone or a few applicators are connected to the fluid circulation system.

In a further embodiment of the applicator, the infusion of fluid intothe proximal tissue adjacent the desired heating zone from the fluidflow space in the applicator may be provided by eliminating the fluidflow return path from the applicator, either by blocking the fluidreturn path or by removing the fluid return path inside the applicatorbody and providing a lower flow rate of cooling fluid to the applicator,such as by providing either a lower flow rate fluid pump or by providinga fluid gravity drip line that is typical if intravenous (IV) fluidapplications. FIG. 16 is a vertical section similar to that of FIG. 10but without a cooling fluid outlet and without the guide sleeve 40, andadditionally including the one or more small openings, holes, or slots190 extending through the outer conductive sleeve 18 as shown in FIG.14. However, in this embodiment of the applicator, the flow of coolingfluid into and through the cooling fluid space 82 is limited to thefluid that flows through the openings 190 into the proximal tissueadjacent the proximal end of the desired heating zone. Again, thepurpose of injecting fluid into the proximal tissue adjacent the desiredheating zone is to hydrate or wet the proximal tissue adjacent thedesired heating zone so it does not dry. This hydrating of the proximaltissue counteracts the drying of the tissue that would otherwise occurand tends to maintain the normal dielectric constant of this proximaltissue. This reduces the amount of microwave energy that travels downthe proximal portion of the applicator, which in FIG. 16, reduces theamount of microwave energy that travels from the desired heating zonedown the outer conductive sleeve 18. With this embodiment, the coolingof the applicator by the cooling fluid flowing through the cooling fluidspace 82 along the outside of coaxial transmission line 26 and theinside of outer conductive sleeve 18 is significantly reduced from thecooling provided in the embodiments of FIGS. 10 and 14 since the flow ofcooling fluid is significantly reduced. As indicated, the typical flowrate within the applicator body of FIGS. 10 and 14 having a fluid inletand a fluid outlet is in the range of 20 to 40 ml/minute. The rateneeded to infuse fluid into the proximal tissue adjacent the desiredheating zone is less than 10 ml/minute and typically in the range ofonly 1 to 6 ml/minute. Therefore, it is only the significantly less flowin the range of 1 to less than 10 ml/minute of cooling fluid that flowsthrough the cooling fluid space 82. However, for many applications ofthe applicator, this is all that is needed during treatment.

FIG. 17 is a vertical section similar to that of FIG. 2, but without acooling fluid outlet and without the guide sleeve 40, and additionallyincluding the one or more small openings, holes, or slots 190 extendingthrough the outer conductive sleeve 18 as shown in FIG. 15. Again, aswith the embodiment of FIG. 16, in this embodiment of the applicator,the flow of cooling fluid into and through the cooling fluid space 82 islimited to the fluid that flows through the openings 190 into theproximal tissue adjacent the proximal end of the desired heating zone.As with the embodiment of FIG. 15, if desired, the reduced outerdiameter end portion 84 of shunt 20 could be shortened to allow openingsthrough the outer conductive sleeve 18 to be positioned closer to theimmediate proximal end of the desired heating zone 25 or passages couldbe provided in the reduced outer diameter end portion 84 of shunt 20leading to openings through outer conductive sleeve 18 closer to theimmediate proximal end of the desired heating zone 25.

Since the flow rate of fluid to the applicators of FIGS. 16 and 17 isreduced to only that needed for hydration of the proximal tissueadjacent the desired heating zone, i.e., in the range of 1 to less than10 ml/minute, the fluid supply systems used to supply fluid to suchapplicators need only to supply fluid at the reduced flow rate, and donot need provision to accept return fluid from the applicators. FIG. 18is a schematic representation showing a fluid supply system similar tothat of FIG. 11, but without the cooling fluid return line 186 and thecooling fluid return connectors 168. Fluid pump 170 is selected tosupply cooling fluid at the lower flow rate, typically between about 1and less than 10 ml/minute, rather than the 20 to 40 ml/minute providedby the pump of FIG. 11. Further, since control of injected fluid may bemore critical with only fluid injection than with fluid flow through thecooling fluid space 82 with return to the fluid reservoir, andparticularly when a large variable number of applicators can be attachedto the fluid circulation system, such as more than the three possiblewith the system shown, pressure and/or flow sensors and a pumpcontroller can be provide to measure and maintain the pressure and/orflow rate of the fluid supplied to connected applicators sufficient toensure desired fluid injection to the proximal tissue adjacent thedesired heating zone through the connected applicators when a largenumber of applicators are connected to the fluid circulation systemwithout providing too much pressure and fluid injection when only one ora few applicators are connected to the fluid circulation system. Itshould be noted that since the fluid supply system of FIG. 11 includescooling fluid return connectors 168 which include one way valves so areblocked if no cooling fluid outlet connectors are connected thereto,such system of FIG. 11 would operated similarly to that of FIG. 18 andcould be used in place of the system of FIG. 18 for the applicators ofFIGS. 16 and 17 with only adjustment of the fluid output pressure and/orflow rate, if necessary.

FIG. 19 is a schematic representation showing a fluid supply systemwithout a pump or cooling fluid return line and cooling fluid returnconnectors. The fluid supply system of FIG. 19 uses a fluid gravity dripline that is typical of intravenous (IV) fluid applications. In such acase the fluid flow rate from the gravity drip line can be set to apredetermined flow rate that would provide the typically desired flowrate in the range of 1 to 6 ml/minute of fluid flow to each of theapplicators attached to the fluid supply system. Such flow rate from thefluid reservoir (IV bag) would be adjusted each time the number ofapplicators attached to the system is changed.

Whereas the invention is here illustrated and described with referenceto embodiments thereof presently contemplated as the best mode ofcarrying out the invention in actual practice, it is to be understoodthat various changes may be made in adapting the invention to differentembodiments without departing from the broader inventive conceptsdisclosed herein and comprehended by the claims that follow.

The invention claimed is:
 1. A microwave applicator for insertion intoliving body tissue for heat treatment of diseased tissue within theliving body tissue, the microwave applicator comprising: an elongateapplicator body having an insertion end for insertion into a tissueregion of the living body and an attachment end for attachment to asource of microwave energy; an antenna for radiating microwave energydisposed toward the insertion end of the elongate applicator body, saidantenna, when radiating microwave energy, creating a primary energyradiation zone; a microwave energy transmission line disposed within theelongate applicator body to conduct the microwave energy from theattachment end of the elongate applicator body to the antenna, saidmicrowave energy transmission line having an inner conductor and anouter conductor; an outer electrically conductive sleeve extendingaround and spaced from the outer conductor of the microwave energytransmission line to form an outside of a portion of the elongateapplicator body and to provide a cooling fluid space between the outerconductor of the microwave transmission line and an inside surface ofthe outer electrically conductive sleeve; a cooling fluid in the coolingfluid space; an electrically conductive applicator tip forming theinsertion end of the elongate applicator body and electrically coupledto the inner conductor of the transmission line; dielectric materialpositioned between and joining the outer electrically conductive sleeveand the electrically conductive applicator tip to electrically insulatethe electrically conductive applicator tip from the outer electricallyconductive sleeve and from the outer conductor of the microwavetransmission line so that the electrically conductive applicator tip iselectrically insulated from the outer electrically conductive sleeve andfrom the outer conductor of the microwave transmission line, and aplurality of openings extending through the outer electricallyconductive sleeve from the cooling fluid space for injecting the coolingfluid from the cooling fluid space into an area of tissue to be hydratedsurrounding the elongate applicator body and selectively positionedadjacent to the elongate applicator body extending along the elongateapplicator body from approximately adjacent to the end of the primaryenergy radiation zone toward the attachment end of the elongateapplicator body; wherein the cooling fluid circulates into and out ofthe cooling fluid space and the plurality of openings thereby limiting atail of the primary energy radiation zone causing formation of asubstantially spherical ablation zone.
 2. A microwave applicator forinsertion into living body tissue, according to claim 1, additionallyincluding a guide sleeve positioned concentrically around and spacedfrom the outer conductor of the microwave energy transmission line andthe inside surface of the outer electrically conductive sleeve to divideat least a portion of the cooling fluid space into an inner coolingfluid space along the outer conductor of the microwave energytransmission line and an outer cooling fluid space along the insidesurface of the outer electrically conductive sleeve, said inner coolingfluid space communicating with said outer cooling fluid space wherebysaid guide sleeve is adapted to guide flow of the cooling fluid withinthe cooling fluid space to cool the microwave energy transmission lineand the outer electrically conductive sleeve.
 3. A microwave applicatorfor insertion into living body tissue according to claim 2, wherein thedielectric material extends between the outer electrically conductivesleeve and the outer conductor of the coaxial microwave transmissionline to form an end of the cooling fluid space toward the insertion endof the applicator.
 4. A microwave applicator for insertion into livingbody tissue according to claim 3, wherein the cooling fluid spaceterminates along the length of the microwave energy transmission lineprior to reaching the antenna.
 5. A microwave applicator for insertioninto living body tissue according to claim 2, additionally including anelectrically conductive shunt extending between the outer electricallyconductive sleeve and the outer conductor of the coaxial microwavetransmission line to form an end of the cooling fluid space toward theinsertion end of the applicator and forming an extension of the outerelectrically conductive sleeve, the dielectric material being positionedbetween and joining the electrically conductive shunt and theelectrically conductive tip to electrically insulate the electricallyconductive tip from the electrically conductive shunt, the outerelectrically conductive sleeve, and the outer conductor of the microwavetransmission line.
 6. A microwave applicator for insertion into livingbody tissue according to claim 5, wherein the cooling fluid spaceterminates along, the length of the microwave energy transmission lineprior to reaching the antenna.
 7. A microwave applicator for insertioninto living body tissue according to claim 2, additionally including ahandle from which the outer electrically conductive sleeve, microwaveenergy transmission line, and the guide sleeve extend.
 8. A microwaveapplicator for insertion into living body tissue according to claim 7,wherein the handle includes an inlet for connection to a source ofcooling fluid and an outlet for outflow of the cooling fluid, andwherein, when the cooling fluid is supplied through the cooling fluidinlet, the cooling fluid flows into the cooling fluid space in theelongate applicator body from the handle and a portion thereof returnsfrom the cooling fluid space in the elongate applicator body into thehandle.
 9. A microwave applicator for insertion into living body tissueaccording to claim 8, additionally including a cooling fluid circulationsystem having at least one fluid supply connector adapted to beconnected to the cooling fluid inlet and at least one fluid returnconnector adapted to be connected to the cooling fluid outlet, said atleast one fluid supply connector including a normally closed shut offvalve which opens when connected to the cooling fluid inlet and the atleast one fluid return connector including a one way flow valve allowingflow only into the at least one fluid return connector.
 10. A microwaveapplicator for insertion into living body tissue according to claim 1,additionally including a handle from which the outer electricallyconductive sleeve and the microwave energy transmission line extend, andwherein the handle includes an inlet for connection to a source ofcooling fluid, and wherein, when the cooling fluid is supplied throughthe cooling fluid inlet, the cooling fluid flows into the cooling fluidspace in the elongate applicator body from the handle and at least aportion thereof flows from the cooling fluid space in the elongateapplicator body through the one or more openings into the tissue to behydrated.
 11. A microwave applicator for insertion into living bodytissue according to claim 10, additionally including a cooling fluidcirculation system having at least one fluid supply connector adapted tobe connected to the cooling fluid inlet, said at least one fluid supplyconnector including a normally closed shut off valve which opens whenconnected to the cooling fluid inlet to allow flow of fluid into thecooling fluid inlet.
 12. A microwave applicator for insertion intoliving body tissue according to claim 1, wherein the elongate applicatorbody includes an inlet for connection to a source of cooling fluid, andwherein, when the cooling fluid is supplied through the cooling fluidinlet, the cooling fluid flows into the cooling fluid space in theelongate applicator body and at least a portion thereof flows from thecooling fluid space in the elongate applicator body through the one ormore openings into the tissue to be hydrated.
 13. A microwave applicatorfor insertion into living body tissue according to claim 1, wherein theelectrically conductive applicator tip is metal.
 14. A microwaveapplicator for insertion into living body tissue according to claim 13,wherein the electrically conductive applicator tip is stainless steel.15. A microwave applicator for insertion into living body tissueaccording to claim 13, wherein the electrically conductive applicatortip is brass.
 16. A microwave applicator for insertion into living bodytissue according to claim 1, wherein the outer electrically conductivesleeve is metal.
 17. A microwave applicator for insertion into livingbody tissue according to claim 16, wherein the outer electricallyconductive sleeve is stainless steel.
 18. A system for microwave therapyfor heat treatment of diseased tissue within a living body, comprising:a microwave applicator for insertion into living body tissue, accordingto claim 1; and a fluid reservoir in communication with the coolingfluid space to supply the cooling fluid to the cooling fluid space, saidfluid reservoir positioned and adapted to allow fluid to flow by gravityfrom the fluid reservoir to the cooling fluid space.
 19. A system formicrowave therapy for heat treatment of diseased tissue within a livingbody, according to claim 18, wherein the fluid reservoir is a standardfluid filled IV bag with a fluid gravity drip line.
 20. A system formicrowave therapy for heat treatment of diseased tissue within a livingbody, comprising: a microwave applicator for insertion into living bodytissue, according to claim 1; a fluid reservoir; and a pump to pumpfluid from the fluid reservoir to the cooling fluid space.